Method of removing suspended acidic or alkaline pulverulent particles from gases



Nov. 19, 1968 J. PALLINGER 3,411,864

METHOD OF REMOVING SUSPENDED ACIDIC OR ALKALINE PULVERULENT PARTICLESFROM GASES Filed July 9, 1964 j f P ELF liar United States Patent METHODOF REMOVING SUSPENDED ACIDIC 0R ALKALINE PULVERULENT PARTICLES FROMGASES Josef Pallinger, Vienna, Austria, assignor to Waagner- BiroAktiengesellschaft, Vienna, Austria Filed July 9, 1964, Ser. No. 381,320Claims priority, application Austria, July 10, 1963, A 5,538/63 11Claims. (Cl. 23-2) ABSTRACT OF THE DISCLOSURE Acidic or alkalinepurverulent particles suspended in a gas are washed out of the latterwith a washing liquid so that the spent Washing liquid, not withstandingthe acidic or alkaline nature of the pulverulent impurities will besubstantially neutral, by introducing into the gaseous suspension ofnon-fluid and generally solid acidic or alkaline impurities apul-verulent alkaline or acidic ma- The present invention relates to agas washing method and device and, more particularly, is concerned withpuritying gases, especially dust-containing gases, such as are formed inthe operation of metallurgical furnaces and combustion devices.

It is an object of the present invention to provide a method and devicefor washing such gases and gaseous suspensions of finely subdividedparticles so as to obtain a spent washing or scrubbing liquid which issubstantially neutral irrespective of the acidity or alkalinity of thegas or suspension which is subjected to such scrubbing or washing.

It is a further object of the present invention to provide a method anddevice for cleaning waste gases and particularly solid particlescontaining waste gases by means of a washing liquid so that in a simpleand economical manner a substantially neutral spent washing liquid isobtained.

It is a further object of the present invention to obtain in a gaswashing process a substantially neutral spent washing liquid withouthaving to adjust the pH of the washing liquid after the same has been incontact with the gas to be purified.

Other objects and advantages of the present invention will becomeapparent from a further reading of the description and of the appendedclaims.

With the above and other objects in view, the present invention isconcerned with a method of washing a gaseous suspension containingacidic impurities, comprising the steps of introducing into the gaseoussuspension an alkaline pulverulent neutralizing agent for the acidicimpurities, and contacting the thus formed neutralizing agent-containingsuspension with an aqueous washing liquid so as to form a purified gasand a spent washing liquid containing the impurities and beingsubstantially neutral due to the introduction of the neutralizing agent.

More particularly, the present invention contemplates a method ofwashing a gaseous suspension containing acidic impurities, comprisingthe steps of introducing into the gaseous suspension calcium carbonateas a salt 3,411,864 Patented Nov. 19, 1968 adapted at an elevatedtemperature to be split into a basic oxide and a volatile acid residue,the basic oxide being adapted to neutralize the acidic impurities,subjecting the thus formed mixture to the elevated temperature so as toform the volatile acid and the basic oxide adapted to act as aneutralizing agent for the acidic impurities, and contacting the thusformed neutralizing agent-containing suspension with an aqueous washingliquid so as to form a purified gas and a spent washing liquidcontaining the impurities and being substantially neutral due to theintroduction of the neutralizing agent.

The present invention also includes a gas purification devicecomprising, in combination, conduit means having inlet and outlet endsfor passing therethrough a gaseous suspension of solid particlesincluding constituents which with a washing liquid will give a reactionother than neutral, introduction means communicating with the conduitmeans at a point spaced from the inlet and outlet ends thereof forintroducing into the same a pulverulent neutralizing agent for thegaseous suspension, gas washing means operatively connected to theoutlet end of the conduit means for washing the neutralizingagentcontaining suspension with a Washing liquid to form a washed gasand a substantially neutral spent washing liquid, and separating meansfor separating the thus washed gas from the spent washing liquid.

According to one preferred embodiment, the present invention includes ina gas purification device, in combination, reactor means for forming acombustible gaseous suspension of solid particles including constituentswhich with a washing liquid will give a reaction other than neutral,combustion means for burning the combustible gaseous suspension andincluding injector means for injecting into the combustible suspension apulverulent neutralizing agent suspended in combustion air so as to formin the combustion means a burnt gas having solid particles suspendedtherein, washing means for washing the suspension of solid particles inburnt gas with a washing liquid forming a washed gas and a spent washingliquid which is substantially neutral due to the injection of theneutralizing agent, conduit means for passing gaseous suspension fromthe reactor means to the combustion means and from the combustion meansto the washing means, and separating means for separating washed gas andspent washing liquid from each other.

Thus, according to the present invention, a pulverulent neutralizingagent, for instance, a salt or an oxide is introduced into the gaseswhich are released from the reactor, for instance, from a metallurgicalfurnace, and the thus formed mixture is then contacted with the washingliquid.

The washing liquid will thus contact a gas which contains, for instance,acidic components either in gaseous form or in the form of suspendedsolids, and which also contains pulverulent neutralizing agent. Eitherduring the washing, or at least partly prior thereto, a reaction willtake place between the acidic constituents and the neutralizing agent soas to neutralize the acidic constituents and thus the wash water willremain neutral and will not be acidified by the presence of acidicconstituents in the gas or gaseous suspension of solids which is to bewashed.

Generally, the gas or suspension will contain acidic constituents andthe neutralizing agent will be a salt or oxide of alkaline reaction,however, it is of course also possible to utilize the present inventionfor neutralizing alkaline gases or suspensions with an acidicneutralizing agent.

While the present invention also could be applied to a gas of acidic oralkaline reaction which does not carry any suspended solids, it isprimarily contemplated to be employed in connection with the removal ofdust or suspended solids from gases which emanate from a variety ofreaction devices, such as metallurgical furnaces, converters, orcombustion devices.

The novel features which are considered as characteristic for theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of specificembodiments when read in connection with the accompanying drawing, inwhich the figure is a schematic elevational view of a device accordingto the present invention for purifying gases emanating from a steelconverter, combined with combusting such gases and utilizing the heatcontent of the same.

A converter 1 is shown from the opening 2 of which gases will bedischarged upon refining of steel in the converter 1. These gases arecaught or received by hood 3 while simultaneously air will flow intohood 3 through the annular opening 4 between converter 1 and hood 3.Through an opening 5, the gases pass into boiler 6, in contact with thewater or steam tubes therein. Opening 5 can be closed by means of gatevalve 7 and immediately behind gate valve 7 are nozzles 8 for blowingsecondary air into the boiler. This secondary air serves for ignitingthe combustible gas which is introduced through hood 3 and for thoroughmixing of the converter gases with the additional air introduced throughopening 4. Turbulence is created and serves for an intimate mixing ofthe gases, combustion of which will be practically completed when thegases leave boiler 6 at its upper end portion. The gases, which containsuspended solids, flow then through conduits 9 and 10 whereby, asillustrated, a super-heater 11 and a preheater 12 are arranged inconduit 10. After the gases have passed in contact with preheater 12,they are introduced into the washer 13 in which, through nozzles 14, awashing liquid is passed in contact with the gases. The waste gaseswhich have been purified by contact with the washing liquid, generallywater, and from which solid suspended particles have been removed, passthen through flue 15 into a smoke stack (not shown).

The air which is blown into the boiler through nozzles 8 is ambient airwhich is introduced through conduit 16 into blower 17. The air iscompressed in blower 17 and flows through a nozzle 18, for instance,into an ejector device 19 wherein a suction effect is created which willserve to carry along pulverulent materials, for instance, pulverulentneutralizing agents for acidic converter gases, such as calcium oxide,calcium carbonate or the like which have been ground to greater orlesser degree of fineness. This pulverulent neutralizing agent, forinstance, calcium carbonate, is stored in hopper 20 and reaches ejector19 through a dosing device 21 so that controlled quantities of thepulverulent neutralizing agent are sucked into the ejector and will thenflow together with secondary air through conduit 22 to nozzles 8.

Thus, the secondary air which is introduced into the boiler forcombustion of the converter gases, is charged with the solidneutralizing agent and the solid neutralizing agent together with theWaste gases and the converter dust container in the same will pass intowashing device 13.

In washing device 13, the neutralizing agent as well as the converterdust will be washed out of the waste gases before the waste gases arereleased through flue 15-.

In this manner, it is possible to maintain the pH of the washing liquidat all times within the desired limit of between 6 and 8.

The spent washing liquid leaves Washer 13 at its outlet 23 and is passedby way of pump 24 into clarifier 25 in which sludge is separated fromthe liquid. The clear liquid flows then to storage tank 26 and is thenrecycled by means of pump 28 through conduit 27 to the nozzles 14 ofWasher 13.

The desired water level is maintained in storage tank 26 by introducinginto the same in conventional manner the amount of fresh water requiredfor this purpose. The heavy sludge is discharged from converter 25.

Under certain operating conditions, it has been found advantageous tointroduce the neutralizing agent, such as calcium carbonate or calciumoxide as relatively large particles, particularly when the neutralizingagent is introduced into an area of very high temperatures. Preferably,the lime dust or the like is injected into a zone where the waste gasesare of very high temperature, either initially or due to combustion ofthe same, and quite obviously, the neutralization reaction will befacilitated by reduction of the particle size of the neutralizing agent.However, if the gases in the hot zone wherein the neutralizing agent isintroduced, are sufliciently hot, then coarser lime dust, for instance,wil be split up by exposure to such high temperature and thus a desiredsmall particle size will be obtained even though the initiallyintroduced lime dust may have been of coarser grain size.

The invention is not limited to the illustrated device and the manner ofoperation of the same which has been described by way of example.

Thus, it is also possible to introduce the neutralizing agent, such ascalcium carbonate, into the reactor, for instance, converter 1 undersuch operating conditions that the desired oxide and a volatile gaseousresidue will be formed, for instance, calcium oxide as the basic oxideand carbon dioxide as the volatile acidic residue in the case ofintroducing calcium carbonate. The salt or oxide is then carried alongby the gases flowing from the reactor, such as converter 1, due to thehigh speed of flow of such gases.

It is also possible to introduce the neutralizing agent into the boilerflue through a dust mill or sprinkler stoker whereby mixing of theconverter or the like Waste gases and the pulverulent neutralizing agentwill take place within the boiler fiue.

The present process and device has considerable advantages over priorart arrangements according to which in the case of acidic waste gasesalkaline substances, such as calcium carbonate are added to the feedwater of the washing device, for instance, to neutralize S0 or S0 inorder to keep the wash water at a pH approximating 7.

For instance, in some cases, when the sulfur content of the waste gasesis high, so much lime would have to be added to the scrubbing liquidthat the limit of solubility of lime in water would be reached or evenexceeded. This is one of the problems solved according to the presentinvention, which provides that the required amount of lime is introducedin pulverulent form into the gas stream for the purpose of keeping thewash water or scrubbing liquid neutral. In this manner, the amount ofpulverulent lime or the like can be so proportioned that any amount ofacidic constituents can be washed out and by the injection of theneutralizing agent in pulverulent form into the hot waste gases stillneutralization of the scrubbing liquid is achieved.

Neutralization may take place in the gas flow, i.e. prior to contactwith the washing liquid, as well as in the scrubber upon contact withthe washing liquid (generally water).

Neutralization of the wash water could be achieved in the abovedescribed manner, for instance, in connection with the purification ofconverter gas carrying converter dust which contained 1.7% CaO, 0.3%MgO, 3.4% S03 and FB2(SO4)3H2SO4'2H20.

Basically, the present invention proposes introduction of theneutralizing agent in solid pulverulent form anywhere between thereaction vessel in which the gases which are to be cleaned are formed(or even in the reaction vessel) and the washing device. The optimumpoint of introduction of the pulverulent neutralizing agent will dependon temperature and flow conditions, as well as on the chemicalcompositions of the gas, the dust carried by the same and theneutralizing agent. Thus, there may also exist conditions under which itis advantageous to introduce the neutralizing agent at high temperaturein the form of a very finely subdivided dust, or at somewhat lowertemperature as coarser particles.

The addition of neutralizing agent should be controlled in such a mannerthat the waste wash Water will be substantially neutral withoutburdening the recycling wash water with excessive amounts ofneutralizing agent. Thus, it should be possible to temporarily interruptthe addition of neutralizing agent when the concentration of the same inthe recycling wash water exceeds a desired value.

It should also be possible, instead of completely interrupting theaddition of neutralizing agent, to reduce the amount thereof which isintroduced per unit of time. By controlling the addition of theneutralizing agent depending on the condition of the washing liquid, itis advantageous to measure the pH value of the washing liquid leavingthe washer at outlet 23 and based thereon to control in an automaticmanner known per se the amount of neutralizing agent which will beadded. Thus, pH meter 31 may be located in the conduit leading fromwashing device 13 to pump 24 and may serve to actuate dosing device 32.

Particularly if the neutralizing agent is introduced into the gas nearits point of origin and relatively distant from the washer, as has beenillustrated in the drawing, and when, consequently, the neutralizingagent is introduced into hot gas, a neutralizing reaction will takeplace between the neutralizing agent and the hot gas and/or the dustcarried by the same already long before the gas reaches washer 13.

Furthermore, the introduction of the neutralizing agent may also becarried out jointly with the introduction of a fuel into burner 6 orjointly with the introduction of primary combustion air into the same.

The term coarser dust or coarser particles is used herein to denoteparticles of a size of 200 microns or larger, while particles of a sizesmaller than 200 microns are referred to as very finely subdivided dust.When the pulverulent neutralizing agent, for instance calcium carbonate,is blown into gas having a temperature of at least 1000 C. i.e. at arelatively high elevated temperature, due to the temperature stress, theparticles of the neutralizing agent will be broken up into smallerparticles and thus will act more efiectively due to the larger surfacearea relative to the volume of the individual smaller particles.

However, if the pulverulent neutralizing agent is to be introduced intogas having a temperature of less than 1000" C., then it is preferred touse very finely subdivided dust, or particles of the neutralizing agentwhich have a size smaller than 200 microns since at such relatively lowtemperatures, i.e. a temperature of below l000 C., the heat stresseswill not sufiice to cause further breakdown in the particle size.

By introducing for instance lime into a zone of higher temperature, forinstance into converter or reaction vessel 1, the greatest degree ofsplitting of the particles can be achieved and thus the reducing agentwill become available in most finely subdivided form and consequentlywill be of higher reactivity.

By way of example, it may be described that a conventional gas washingdevice 220 cubic meters per hour of water were used for purifying wastegases. The waste gases carried 100 kg. of sulfur per hour, the latterbeing chemically bound in various manners, for instance as S0 The wetwashing device removed about 80 90% of the sulfur content of the wastegas and thus, theoretically, should have required about 300 kg. ofcalcium carbonate per hour for neutralizing the wash water.

However, it was found that even by introducing into the wash water twicethe theoretically required amount of calcium carbonate, i.e. 600 kg. perhour, it was not possible to obtain a neutral spent washing liquid. Infact,

the pH of the washing liquid leaving the device was between 2 and 3.

However, by blowing 300 kg. per hour of calcium carbonate into the hotstream of gas and subsequently subjecting the gas to washing in the samemanner as before, the runoff from the washing device was completelyneutral, having a pH of 7.

This comparison will show greater effectiveness of blowing the requiredamount of lime or other neutralizing agent in pulverulent form into thehot gas stream. In the given case it was also found that the investmentrequired for neutralizing the gas by blowing neutralizing agent into thesame amounted to only about one-tenth of the investment required forneutralizing the washing liquid in accordance with the conventionalprocess.

In the herein described case, calcium carbonate particles having aparticle size greater than 200 microns were blown into acidic gas havinga temperature of about 1300 C.

Substantially similar results are obtained in the case of neutralizingalkaline waste gases by introducing acidic neutralizing agents into thesame.

Since sludge sedimentation in the clarifier is carried out in a moreeconomical manner at neutral pH, acidic neutralizing agents were blowninto a stream 'of hot alkaline waste gas. In this manner neutralizationand sedimentation could be carried out much more economically than byintroducing the acidic neutralizing agent into the wash water. As theacidic neutralizing agent, sulfur chemically bound in any suitablemanner was introduced into the alkaline gas. In this manner, it waspossible to use installations Which did not require any specificprotection against acid corrosion.

As has been pointed out above, coarse particles having a particle sizeof 200 microns or more will disintegrate into smaller particles due toheat stresses when such coarse particles are introduced into arelatively hot stream of gas, having a temperature of 1000 C. or more.For instance, by introducing lime having a particle size of up to mm.into a reactor in which a temperature of about 1300 C. prevailed, thelime was subdivided into particles of the magnitude of 200 microns. Thiseffect, i.e. the comminution of coarser particles by exposing the sameto high temperatures will, with respect to acidic as well as alkalineneutralizing agents, eliminate the necessity for employing mechanicalcomminution devices.

In another installation, in order to burn CO, secondary air had to beintroduced under high pressure and it was found advantageous tointroduce the neutralizing agent dispersed in the secondary air so thatthe neutralizing agent was blown into the crude gas at high pressuretogether with the secondary air.

It will be understood that each of the elements described above, or twoor more together, may also find a useful application in other types ofwaste gas purification devices differing from the types described above.

While the invention has been illustrated and described as embodied in awaste gas purifying device combined with a boiler arrangement, it is notintended to be limited to the details shown, since various modificationsand structural changes may be made without departing in any Way from thespirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can by applying current knowledgereadily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this inventionand, therefore, such adaptations should and are intended to becomprehended within the meaning and range of equivalence of thefollowing claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. A method of washing a gas containing solid, at least partiallysoluble impurities adapted to be washed out with,

and at least partially dissolved in, a washing liquid and which withsaid washing liquid will give a reaction other then neutral, comprisingthe steps of introducing into said gas a pulverulent neutralizing agentfor said impurities which is at least partially soluble in said washingliquid; contacting the thus formed neutralizing agent-containing mixturewith a washing liquid so as to wash out said impurities and saidneutralizing agent and at least partially dissolve the same, therebypurifying said gas and forming a substantially neutral spent washingliquid; and separating the thus purified gas from said spentsubstantially neutral washing liquid.

2. A method of washing a gaseous suspension of finely subdividednon-fluid, acidic impurities, comprising the steps of introducing intosaid gaseous suspension an alkaline pulverulent neutralizing agent forsaid acidic impurities; and contacting the thus formed neutralizingagentcontaining suspension with an aqueous washing liquid in which saidacidic impurities and said neutralizing agent are at least partiallysoluble so as to form a purified gas and a spent washing liquidcontaining said impurities and being substantially neutral due to saidintroduction of said neutralizing agent.

3. A method of washing a gaseous suspension of finely subdivided,non-fluid, acidic impurities, comprising the steps of introducing intosaid gaseous suspenson a salt adapted at an elevated temperature to besplit into a basic oxide and a volatile acid residue, said basic oxidebeing adapted to neutralize said acidic impurities; subjecting the thusformed mixture to said elevated temperature so as to form said volatileacid and said basic oxide adapted to act as a neutralizing agent forsaid acidic impurities; and contacting the thus formed neutralizingagent-containing suspension With an aqueous washing liquid in which saidacidic impurities and said basic oxide are at least partially soluble soas to form a purified gas and a spent washing liquid containing saidimpurities and being substantially neutral due to said introduction ofsaid neutralizing agent.

4. A method of washing a combustible gaseous suspension including finelysubdivided, non-fiuid, acidic impurities, comprising the steps ofintroducing into said gaseous suspension a suspension in air of analkaline neutralizing agent for said acidic impurities; subjecting thethus formed mixture to combustion so as to form a neutralizingagent-containing gaseous suspension of solid particles; and contactingthe thus formed neutralizing agent-containing suspension with an aqueouswashing liquid in which the non-fluid constituents of said suspensionare at least partially soluble so as to form a purified gas and a spentwashing liquid containing said impurities and being substantiallyneutral due to said introduction of said neutralizing agent.

5. A method of washing a gaseous suspension including finely subdivided,non-fluid, acidic impurities, comprising the steps of introducing intosaid gaseous suspension a relatively coarse pulverulent alkalineneutralizing agent for said acidic impurities adapted to split at anelevated temperature into particles of smaller size; subjecting the thusformed mixture to said elevated temperature so as to reduce the particlesize of said neutralizing agent; and contacting the thus formedneutralizing agent-containing suspension with an aqueous washing liquidin which the non-fluid constituents of said suspension are at leastpartially soluble so as to form a purified gas and a spent washingliquid containing said impurities and being substantially neutral due tosaid introduction of said neutralizing agent.

6. A method of washing a gaseous suspension including finely subdivided,non-fluid, acidic impurities, com- 8 acid residue, said basic oxidebeing adapted to neutralize said acidic impurities; subjecting the thusformed mixture to said elevated temperature so as to form said volatileacid and said basic oxide adapted to act as a neutralizing agent forsaid acidic impurities; and contacting the thus formed neutralizingagent-containing suspension with an aqueous washing liquid in which saidimpurities and said basic oxide are at least partially soluble, so as toform a purified gas and a spent washing liquid containing saidimpurities and being substantially neutral due to said introduction ofsaid neutralizing agent.

7. A method of washing a gaseous suspension including finely subdivided,non-fluid, acidic impurities, comprising the steps of introducing intosaid gaseous suspension pulverulent calcium oxide as a neutralizingagent for said acidic impurities; and contacting the thus formedneutralizing agent-containing suspension with an aqueous washing liquidin which said acidic impurities and said calcium oxide are at leastpartially soluble, so as to form a purified gas and a spent washingliquid containing said impurities and being substantially neutral due tosaid introduction of said neutralizing agent.

8. A method of washing a gaseous suspension including finely subdivided,non-fluid, acidic impurities, comprising the steps of introducing intosaid gaseous suspension at a relatively low elevated temperature afinely subdivided pulverulent neutralizing agent for said acidicimpurities; and contacting the thus formed neutralizing agent-containingsuspension with an aqueous washing liquid in which said acidicimpurities and said neutralizing agent are at least partially soluble,so as to form a purified gas and a spent washing liquid containing saidimpurities and being substantially neutral due to said introduction ofsaid neutralizing agent.

9. A method of washing a gaseous suspension including finely subdivided,non-fluid, acidic impurities which suspension is formed in a reactionvessel, comprising the steps of introducing into said reaction vessel analkaline pulverulent neutralizing agent for said acidic impurities so asto form a neutralizing agent-containing gaseous suspension; withdrawingthe thus formed neutralizing agent-containing suspension from saidreaction vessel; and contacting said withdrawn suspension wit-h anaqueous washing liquid in which said acidic impurities and saidneutralizing agent are at least partially soluble, so as to form apurified gas and a spent washing liquid containing said impurities andbeing substantially neutral due to said introduction of saidneutralizing agent.

10. In a method according to claim 2, the steps 0 determining the pH ofsaid spent Washing liquid and adjusting the amount of alkalinepulverulent neutralizing agent being introduced into said gaseoussuspension so as to maintain said pH within a predeterminedsubstantially neutral range.

11. A method according to claim 2, wherein said gaseous suspension offinely subdivided, non-fluid, acidic impurities consists of the wastegases of a metal converter.

References Cited UNITED STATES PATENTS 1,221,505 4/1917 Bradley et al.23-2 X 2,718,453 9/1955 Beckman 23-2 2,877,086 3/ 1959 Mackay 2322,919,174 12/1959 Pring 23-2 3,310,365 3/ 1967 Dundas et al. 232

FOREIGN PATENTS 435,560 9/1935 Great Britain.

OSCAR R. VERTIZ, Primary Examiner.

EARL C. THOMAS, Assistant Examiner.

